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04-01-2012, 12:27   #1
 
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Cold Spell Prospects and Discussion (January + Early Feb 2012)

Please note that this is an outlook based on two successive runs and increasing evidence that a northerly/north-easterly outbreak is indicated around or in the days following 15 January. It is not a guarantee that colder weather will occur post mid-January, although confidence is growing in relation to such an eventuality.

As indicated elsewhere on this forum, with signs increasing that we could soon see both a displacement and split of the polar vortex we are likely to see models increasingly signal wintry weather, most likely from an Arctic source initially. MT also alluded to this today.

At present it looks like there will be a rise in high pressure to our west and northwest allowing Arctic air to sink south or southwestwards over Ireland and the UK around or just after mid-January i.e. 15-17th Jan. The exact positioning of these highs is not yet written in stone but the aforementioned represents the most likely scenario at this early stage.

Based on current output, daytime temperatures would sink to low single figures. The cold spell could last for quite some time (at least 4-5 days) if high pressure continues to build over Scandinavia and Greenland as the models are presently indicating.

Backedge snow would be likely almost everywhere as the cold front sweeps south across Ireland as the transition begins around the 16-18th. Wintry showers would follow for N, NW and E of the country in particular with some making their way into the Midlands and to the southeast. Elsewhere, it will be dry, bright and sunny with severe overnight air and ground frosts. Temperatures may be a few degrees in the extreme nw and sw as high pressure to our w and nw might result in a slack sw flow.

What beyonds this period remains unclear although there are tentative signs that the weather will briefly become a little less cold before a more continental source of cold air extends over at least the eastern UK.

In the meantime (next 10-12 days), the jetstream remains in control of our weather up to then. It will turn drier over the weekend but it will be wetter at times again next week. Temperatures will be slightly above average for the time of year as a whole over the next 10 days.

(Below) Some charts indicating the change on the cards for the post mid-Jan period. These charts will upgrade and downgrade dramatically over the next few days but there will be general trend toward such a setup in the mid Jan period, most likely around 16-18th.

JET STREAM SHIFT


High pressure blocking


Cold 850hpas

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Last edited by Sleety_Rain; 20-01-2012 at 18:06.
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04-01-2012, 12:48   #2
davidsr20
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Fingers crossed this comes off
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04-01-2012, 13:00   #3
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Same date MArk Vogan is going for as well!

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04-01-2012, 13:01   #4
 
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Same date MArk Vogan is going for as well!
Thought his date was mid-December 2011?
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04-01-2012, 13:03   #5
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Noice. ECM shows the potential of this occuring a bit earlier too. Fingers crossed it is then!

I clicked on the thread without spotting the user who started it, completely assumed it was darkman's Well played, wolf, well played.

Last edited by cherryghost; 04-01-2012 at 13:06.
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04-01-2012, 13:06   #6
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so this is why M.T chose cla-15 for his forecast comp
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04-01-2012, 13:08   #7
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Quote:
Originally Posted by WolfeIRE View Post
Thought his date was mid-December 2011?
He has said alot of dates But his video this month is the same yours. Maybe he just likes the date of the 15th
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04-01-2012, 13:23   #8
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GEFS the only one running with this?
Can't see anything similar on other models
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04-01-2012, 13:33   #9
 
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GEFS the only one running with this?
Can't see anything similar on other models
Because most other models do not go beyond 144-240hrs. However, height rises and movement favourable to the setup suggested by the GEFS are occuring in the latter stages of the ECMWF.

Forgot to post these, by the way. Have not seen this downward trend all winter.






AO doesn;t need to go negative for a blast from the north to affect us but it certainly would help any sustained cold from developing. At least it is trending toward negative in the lead up to mid Jan
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04-01-2012, 13:39   #10
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nice to finally see -8's in the 850hpa even if it is subject to change
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04-01-2012, 14:25   #11
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But is the control run is at a lower resolution and less accuarate than the operational? Plus it is an outlier, i think the operational run will be what actually happens, i.e. what we have now!
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04-01-2012, 14:52   #12
 
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Simon Keeling foresees a colder second half of January.
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04-01-2012, 15:16   #13
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But is the control run is at a lower resolution and less accuarate than the operational? Plus it is an outlier, i think the operational run will be what actually happens, i.e. what we have now!
The operational will flip and flop over the next few days, as M.T has said, so what will happen is very hard to know yet
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04-01-2012, 15:26   #14
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Thanks for the information, what is 'Backedge' snow?
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04-01-2012, 15:33   #15
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Thanks for the information, what is 'Backedge' snow?
Colder air digging in behind a front crossing the country.
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